BDNF and early-onset autosomal dominant Alzheimer disease: In particular, changes in DNA methylation at BDNF promoters I and IV have been detected in Alzheimer’s disease (AD) (Rao et al., 2012; Xie et al., 2017), major depression (Januar et al., 2015; Kang et al., 2015), and schizophrenia (Ikegame et al., 2013), but such changes have not yet been explored in HD.